We will develop treatment planning procedures for determining dose to soft tissue adjacent to bone when irradiated by photon beams in the energy range of 60CO to 24 MV. Our aim is to improve dosimetric accuracy near bone-tissue interfaces and thereby gain a favorable therapeutic ratio in cancer treatment. Since the current calculation methods are incapable of providing accurate dosimetry near tissue interfaces of different atomic number, errors of the order of 10 to 20% are possible in clinical dosimetry. Our goal is to reduce this dosimetric uncertainty to within 5%. We consider this improvement in dosimetric accuracy to be significant in radiotherapy in terms of control of the disease and treatment complications. We will use three complementary approaches to develop the appropriate algorithms: a) an analytic method which will separately calculate the kerma distribution and the absorbed dose distribution. the latter will be calculated by our analytic model which describes the transport of electrons across and interface between different media. b) experimental investigations and model verification using suitable phantoms and dosimetry methods; and c) Monte Carlo calculations to verify and supplement the analytic model and the experimental data. Our algorithms for interface dosimetry will be incorporated into a commercial treatment planning system. The sofeware will be readily exportable to other radiotherapy facilities having access to CT scanners and low-cost minicomputers.